AstraZeneca’s COVID-19 Vaccine Data Show 79% Efficacy Against Symptomatic Disease


AstraZeneca is preparing to submit its COVID-19 vaccine data to the FDA for emergency use authorization in the coming weeks.


New interim data from AstraZeneca showed that its COVID-19 vaccine candidate had a 79% efficacy rate in preventing symptomatic cases in adults, with an 80% efficacy in those aged 65 and older, the company announced.

The vaccine, AZD1222, also demonstrated a statistically significant vaccine efficacy of 100% at preventing severe disease and hospitalization in the analysis. Regarding safety, the results demonstrated that the vaccine was well tolerated. An independent data safety monitoring board (DSMB) did not identify any safety concerns related to the vaccine, including no increased risks in its specific review of thrombotic events, as well as cerebral venous sinus thrombosis with the assistance of an independent neurologist.

Many European countries recently temporarily suspended use of AZD1222 due to reports of serious, but rare, cases of blood clots. In its safety review, the DSMB did not report any increased risk of thrombosis or events characterized by thrombosis among the 21,583 participants receiving at least 1 dose of the vaccine.

AstraZeneca will continue to analyze the data and prepare for submission to the FDA for emergency use authorization in the coming weeks, the company said.

This interim analysis is based on the US phase 3 trial, D8110C00001, which assessed the safety, efficacy, and immunogenicity of AZD1222 compared with placebo for the prevention of COVID-19 in 32,449 participants across US, Peru, and Chile. The trial included 2 doses administered at a 4-week interval.

The results are based on 141 COVID-19 cases in the trial. AstraZeneca did not provide specific details on how many cases occurred in participants who received the vaccine versus those who received the placebo.

The following is a breakdown of participant demographics in the analysis:

  • 79% White/Caucasian
  • 8% Black/African American
  • 4% native American
  • 22% Hispanic

Additionally, approximately 20% of participants were aged 65 or older and approximately 60% had comorbidities associated with an increased risk for progression of severe disease.

“These findings reconfirm previous results observed in AZD1222 trials across all adult populations but it’s exciting to see similar efficacy results in people over 65 for the first time,” co-lead principal investigator Ann Falsey, MD, professor of medicine at University of Rochester School of Medicine, said in a statement. “This analysis validates AstraZeneca COVID-19 vaccine as a much-needed additional vaccination option, offering confidence that adults of all ages can benefit from protection against the virus.”

Previous trials have shown that an extended interval of up to 12 weeks demonstrated greater efficacy; however, the latest data suggest that administration of the second dose with an interval longer than 4 weeks could further increase efficacy. The vaccine can be stored, transported and handled at normal refrigerated conditions (2-8 degrees Celsius or 36-46 degrees Fahrenheit) for at least 6 months and administered without the need for preparation within existing health care settings.


1. AZD1222 US Phase III trial met primary efficacy end point in preventing COVID-19 at interim analysis. News release. AstraZeneca; March 22, 2021.

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